Arthroplasty implant

ABSTRACT

The invention concerns an arthroplasty implant for providing a joint between first and second members of the body, such as a metatarsophalangeal (MTP) joint, a metacarpophalangeal (MCP) joint or a proximal interphalangeal (PIP) joint. The implant of the invention includes a fist component ( 10 ) defining a concave surface ( 14 ), a second component ( 20 ) defining a convex surface ( 24 ) and an intermediate component ( 32 ) which is located between the first and second components. The intermediate component has a convex surface ( 36 ) which is slidable on the concave surface of the first component to allow articulation between the first component and the intermediate component and a concave surface slidable on the convex surface of the second component to allow articulation between the second component and the intermediate component. A means ( 16, 38; 50, 60 ) is provided to prevent the intermediate component from separating laterally from at least one of the first and second components.

BACKGROUND TO THE INVENTION

THIS invention relates to an arthroplasty implant.

The invention is particularly concerned with arthroplasty implants ofthe wrist and small bones of the hand and foot, such asmetatarsophalangeal (MTP) joint implants, metacarpophalangeal (MCP)joint implants and proximal interphalangeal (PIP) joint implants.

Various types of implants for such joints have been proposed and are inuse. It is however believed that the known implants, most of which areof two part construction, suffer from one disadvantage or other thateither limits their flexibility, load-transmitting ability or lifeexpectancy.

SUMMARY OF THE INVENTION

According to the present invention there is provided an arthroplastyimplant for providing a joint between first and second members of thebody, the implant comprising:

-   -   a first component defining a concave surface and having first        connection means for connecting it to the first body member;    -   a second component defining a convex surface and having second        connection means for connecting it to the second body member;    -   an intermediate component for location between the first and        second components and defining a convex surface which is        slidable on the concave surface of the first component to allow        articulation between the first component and the intermediate        component and a concave surface slidable on the convex surface        of the second component to allow articulation between the second        component and the intermediate component, and    -   means for preventing the intermediate component from separating        laterally from at least one of the first and second components.

The concave surface of the first component and the convex surface of theintermediate component are preferably complementally, sphericallycurved. In the preferred embodiments, the convex surface of the secondcomponent and the concave surface of the intermediate component aredefined by radii of curvature which differ in mutually orthogonaldirections. The length of the convex surface in a direction defined by arelatively large radius of curvature is preferably greater than thelength of that surface in a direction defined by a relatively smallradius of curvature.

In all cases, the first and second components should be capable oftranslation and articulation relative to the intermediate component.

One embodiment of the invention comprises a central projection on theconcave surface of the first component and a central opening in theconvex surface of the intermediate component, the projection in uselocating loosely in the opening to prevent lateral separation of theintermediate and first components.

In another embodiment of the invention one of the first component andthe intermediate component includes a laterally outwardly facingprojection and the other of the first component and the intermediatecomponent includes a laterally inwardly facing recess, the projection inuse interacting with the recess to prevent lateral separation of theintermediate and first components. Typically in this embodiment, thefirst component includes an annular wall bounding the concave surface ofthat component, the peripheral wall being formed with an annularundercut defining the laterally inwardly facing recess, and theintermediate component includes an annular rib defining the laterallyoutwardly facing projection, interaction in use between the rib and theundercut preventing lateral separation of the intermediate and firstcomponents.

Other features of the invention are defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 shows a perspective view of a first component of an arthroplastyimplant according to a first embodiment of the invention;

FIG. 2 shows a side view of the component seen in FIG. 1;

FIG. 3 shows a perspective view of a second component of an arthroplastyimplant according to first embodiment of the invention;

FIG. 4 shows a side view of the component seen in FIG. 3;

FIG. 5 shows a plan view of the component seen in FIG. 3;

FIG. 6 shows a perspective view of an intermediate component of anarthroplasty implant according to the first embodiment of the invention;

FIG. 7 shows a plan view of the intermediate component seen in FIG. 6;

FIG. 8 shows a cross-section at the line 8-8 in FIG. 7;

FIG. 9 shows a cross-section at the line 9-9 in FIG. 7;

FIG. 10 shows a side view of an assembled arthroplasty implant accordingto the first embodiment of the invention with the first and intermediatecomponents in a neutral position before articulation between them;

FIG. 11 shows a similar side view of the assembled arthroplasty implantseen in FIG. 10 after maximum articulation between the first andintermediate components;

FIG. 12 shows a plan view of the assembled arthroplasty implant seen inFIG. 10 after maximum articulation between the first and intermediatecomponents.

FIG. 13 shows a perspective view of the first component of anarthroplasty implant according to a second embodiment of the invention;

FIG. 14 shows a side view of the first component seen in FIG. 13;

FIG. 15 shows a perspective view of the intermediate component of anarthroplasty implant according to the second embodiment of theinvention;

FIG. 16 shows a side view in the direction of the arrow 16 of theintermediate component seen in FIG. 15;

FIG. 17 shows a side view in the direction of the arrow 17 of theintermediate component seen in FIG. 15;

FIG. 18 shows a side view of an assembled arthroplasty implant accordingto the second embodiment of the invention with the first andintermediate components in a neutral position before articulationbetween them; and

FIG. 19 shows a similar side view of the assembled arthroplasty implantseen in FIG. 18 after maximum articulation between the first andintermediate components.

DESCRIPTION OF PREFERRED EMBODIMENTS

The drawings illustrate individual components of preferredmetatarsophalangeal (MTP) joint implants, and the assembled MTPimplants. In each case the implant consists of three individualcomponents.

A first embodiment of the invention is illustrated in FIGS. 1 to 12 ofthe drawings. In this embodiment, FIGS. 1 and 2 illustrate a first,phalangeal component 10 which is connected in use to a phalanx. Itincludes a body 12 formed with a spherically curved, concave surface 14.Projecting centrally from the surface 14 is a conical peg 16 andprojecting rearwardly from the body 12 is a tapered post 18 of squarecross-section. In use, the post 18 is placed and anchored in apredrilled hole in the phalanx.

FIGS. 3 to 5 illustrate a second, tarsal component 20 which is connectedin use to the associated tarsus. It includes a body 22 with a convexlycurved surface 24 and curved skirts 26, 28. The radius of curvature ofthe surface 24 in the view of FIG. 4 is less than the radius ofcurvature in the view of FIG. 5. Projecting rearwardly from the body 22is a tapered post 30 of square cross-section. In use the post 30 isplaced and anchored in a predrilled hole in the tarsus.

Both the phalangeal component 10 and the tarsal component 20 are made inone piece of grade 5 titanium, their curved surfaces 14 and 24 beingprovided with a titanium nitride finish.

FIGS. 6 to 9 illustrate an intermediate component in the form of ameniscus 32 which is located in the assembled MTP implant between thephalangeal and tarsal components 10 and 20. The meniscus 32 is made of alow friction plastic material, in this case an ultra high molecularweight polyethylene (UHMWPE) available under the name ORTHOSOL™. Oneside of the meniscus is formed with a concave surface 34 and theopposite side with a convex surface 36. The convex surface isspherically curved and is formed centrally with a conical recess orsocket 38. The concave surface 34 is not spherical. The radius ofcurvature of the surface 34 in FIG. 8, which matches radius of curvatureof the surface 24 in FIG. 4, is less than the radius of curvature of thesurface 34 in FIG. 9, which matches the radius of curvature of thesurface 24 in FIG. 5. It will accordingly be understood that the concavesurface 34 of the meniscus is complemental to the convex surface 24 ofthe tarsal component 20, and that the convex surface 36 of the meniscusis complemental to the concave surface 14 of the phalangeal component10.

FIGS. 10 to 12 illustrate an assembled MTP arthroplasty implant 40,according to the first embodiment of the invention, and consisting ofthe three components 10, 20 and 32. The meniscus 32 is located betweenthe phalangeal and tarsal components 10 and 20 with the various concaveand convex surfaces in cooperating relationship with one another. Thepeg 16 of the phalangeal component is located in the socket 38 of themeniscus 32. In this regard it will be noted that the transversedimension of the peg is somewhat less than the transverse dimension ofthe socket at any given point along the length of the peg and socket.

In FIG. 10, the phalangeal component 10 and the meniscus 32 are at aneutral orientation with one another, i.e. they are axially aligned andno articulation or translation has taken place between them. FIG. 11illustrates the situation after maximum permitted articulation andtranslation has taken place between these components. It will be notedthat in FIG. 11, edge regions of the phalangeal component 10 andmeniscus 32 come into contact with one another, as indicated by thearrow 42. Further articulation in the same sense past this condition isimpossible. The fact that the socket 38 is oversize with respect to thepeg 16 permits translation and maximum articulation to take place, butit will be noted that in FIG. 11 the peg 16 also abuts the side of thesocket 38 to prevent further articulation or translation.

Throughout the permitted range of movement between the phalangealcomponent and the meniscus, the peg 16 remains located in the socket 38.This prevents the meniscus from separating laterally from the phalangealcomponent, i.e. holds the meniscus captive relative to the phalangealcomponent at all times.

In FIGS. 10 and 11, there is no change in the positional relationship ofthe meniscus and the tarsal component 20. Given the complementalcurvature of their respective convex and concave surfaces, it willhowever be understood that these components are free to slide over oneanother and, in doing so, to articulate relative to one another. This isillustrated by FIG. 12, which shows the meniscus, and with it thephalangeal component, after relative sliding, i.e. translation, andarticulation has taken place. The convex surface 24 of the tarsalcomponent 20 is substantially larger than the complemental concavesurface 34 of the meniscus, allowing translation and articulation totake place over a wide range of positions and angles.

A second embodiment of the invention is illustrated in FIGS. 13 to 19 ofthe drawings. In these Figures features corresponding to features seenin FIGS. 1 to 12 are indicated by the same reference numerals.

Notable differences between the first or phalangeal component 10illustrated in FIGS. 13 and 14 and the first component 10 seen in FIGS.1 and 2 are the absence of the central peg 16 and the inclusion of anannular, peripheral wall 52 which bounds the concave surface 14 andwhich is formed with an undercut 50 defining a laterally inwardly facingrecess. The wall 52 and concave surface in combination define acup-shaped receptacle 53.

Another difference between the component 10 of FIGS. 13 and 14 and thatof FIGS. 1 and 2 is the face that the post 18 has a round cross-sectionand is provided at its end with barb formations 54.

The second or tarsal component 20 of the second embodiment is seen inFIGS. 18 and 19. This component differs from the second componentillustrated in FIGS. 3 to 5 in that the post 30 is of roundcross-section and carries barb formations 56 at its end. The structuredefining the convex surface 24 is also slightly different, asillustrated.

It is believed that the barb formations 54 and 56 will be able toprovide better anchorage of the posts 18 and 30 in their respectivepredrilled holes in the phalanx and tarsus respectively.

The intermediate component or meniscus 32 of the second embodiment isillustrated in FIGS. 15 to 17. As will be apparent from FIGS. 16 and 17,the concave surface 34 of this meniscus is similar to that of the firstembodiment. The convex surface 36 of the second embodiment is howeverdefined by a somewhat greater radius of curvature than the correspondingsurface in the first embodiment. Anther difference between the convexsurface 36 of the second embodiment and that of the first embodiment isthe absence of the central recess or socket 38. The meniscus alsocinludes an annular groove 58, with a portion 59 of the meniscus beneaththis groove presenting an annular, outwardly facing rib 60.

FIGS. 18 and 19 illustrated the second embodiment in an assembledcondition. The portion 59 of the meniscus is received in the cup-shapedreceptacle 53. Typically the outer diameter of the rib 60 will be suchthat the portion 59 is either be a very close fit or a press fit throughthe opening defined by the inner rim 63 of the undercut side wall 52. Acomparison of FIGS. 18 and 19 shows how the first component and meniscuscan both articulate and translate laterally relative to one another. Itwill however be understood that throughout the range of permittedtranslation and articulation, the lower portion 59 of the meniscus isheld captive relative to the first component 10 by the undercut sidewall 52. Thus in this embodiment the interaction of the rib 60 and theundercut recess 50 prevents the components from separating laterallyfrom one another.

A comparison of FIGS. 18 and 19 also illustrates the ability of theimplant to accommodate a wide range of translation and articulationbetween the second component 20 and the meniscus.

Referring again to the first embodiment, a comparison of FIGS. 10 and 11on one hand and FIG. 12 on the other hand indicates that articulationand translation between the components can take place in mutuallyorthogonal directions. The range of translation and articulated movementbetween the tarsal component 20 and the meniscus in one direction,illustrated by FIGS. 10 and 11, is greater than the corresponding rangeof movement in the orthogonal direction, illustrated by FIG. 12. Thisfeature is attributable to the shape of the structure defining theconvex surface 24 and is provided for the reason that most small jointsof the hand or foot are designed to flex primarily in one direction.Considering, for instance, a toe joint, the primary flexural movement ofthe toe is towards or away from the foot rather than at right anglesthereto, although at least a small degree of movement in the lattersense must also be accommodated.

FIGS. 18 and 19 only illustrate the primary flexural movement, but itwill be understood that a similar range of movement in the orthogonaldirection is also possible in this embodiment.

In both embodiments the concave surface 34 of the meniscus and theconvex surface of the tarsal component 20 is defined by radii ofcurvature which differ from one another in mutually orthogonaldirection. This feature also contributes to movement in the primarydirection. In the case of the first embodiment compare, for instance,FIGS. 4 and 5 illustrating the tarsal component and FIGS. 8 and 9illustrating the meniscus. In the case of the second component, asimilar comparison may be made between FIGS. 16 and 17 illustrating themeniscus. In each case, it will be understood that sliding movement iseasier in the direction defined by the larger radius of curvature, i.e.the more gentle curvature.

It is believed that the three component implants described above andillustrated in the drawings will provide for substantial flexibility inthe implanted arthroplasty. Also, the relatively large bearing areasbetween the respective components will, it is believed, provide thearthroplasty with substantial longevity. Referring in particular to thephalangeal components 10 and the menisci 32, the fact that thesecomponents are retained in their cooperating relationship either by theinteraction of the peg 16 and socket 38 or by the interaction of theportion 60 and the undercut 50 means that there still remains a largebearing area between the components to transmit generally axial loading.

Many modifications are possible within the scope of the invention. Forinstance, although it is considered beneficial in the first embodimentfor the peg to abut the side of the socket, as illustrated in FIG. 11,this is not critical to the performance of the implant. In the secondembodiment described above, it is the interaction of an outwardly facingprojection, i.e. the rib 60 and the inwardly facing recess, i.e, theundercut 50, which prevents lateral separation of the phalangealcomponent and meniscus. The rib and recess are included in thephalangeal component and meniscus respectively. It will however beunderstood that the situation could equally well be reversed, with aprojection on the phalangeal component interacting with a recess on theintermediate member. In similar fashion the peg and recess arrangementof the first embodiment could be reversed with the peg on theintermediate component and the recess in the first or phalangealcomponent. Still further the concave and convex surfaces could bereversed so that, for instance, the palangeal component has the convexsurface and the tarsal component has the concave surface, such surfacesinteracting with a concave and convex surfaces respectively on theintermediate member. It is also feasible for means to be provided, eg inthe form of the described peg and recess combination or the describedrib and recess combination, to prevent separation of the intermediatemember from both of the first and second components. It is the intentionthat all such variations are included with the scope of the invention.

Further, while specific mention has been made of MTP arthroplastyimplants, it will be understood that the principles of the invention areequally applicable to other arthroplasty implants, including thosementioned at the outset, typically for the wrist or small bones of thehand or foot.

1-14. (canceled)
 15. An arthroplasty implant for providing a jointbetween a first body member and a second body member, the arthroplastyimplant comprising: a first component defining a concave surface andhaving a first connector connecting the first component to the firstbody member; a second component defining a convex surface and having asecond connector connecting the second component to the second bodymember; and an intermediate component positioned between the firstcomponent and the second component and defining a convex surfaceslidable on the concave surface of the first component to allowarticulation between the first component and the intermediate componentand a concave surface slidable on the convex surface of the secondcomponent to allow articulation between the second component and theintermediate component.
 16. The arthroplasty implant according to claim15 wherein the concave surface of the first component and the convexsurface of the intermediate component are complementally, sphericallycurved.
 17. The arthroplasty implant according to claim 15 wherein eachof the convex surface of the second component and the concave surface ofthe intermediate component is defined by radii of curvature which differin mutually orthogonal directions.
 18. The arthroplasty implantaccording to claim 15 wherein a length of the convex surface of thesecond component in a direction defined by a relatively large radius ofcurvature is greater than a length of the convex surface in a directiondefined by a relatively small radius of curvature.
 19. The arthroplastyimplant according to claim 15 wherein each of the first component andthe second component is capable of translation and articulation relativeto the intermediate component.
 20. The arthroplasty implant according toclaim 15 wherein each of the first component and the second component ismade of grade 5 titanium and each of the concave surface and the convexsurface has a titanium nitride finish.
 21. The arthroplasty implantaccording to claim 15 wherein the intermediate component is made of alow friction plastic material.
 22. The arthroplasty implant according toclaim 21 wherein the plastic material is ultra high molecular weightpolyethylene.
 23. The arthroplasty implant according to claim 15 whereinthe first connector and the second connector each includes a projectingpost locatable in a hole formed in a respective body member.
 24. Thearthroplasty implant according to claim 15 further comprising a centralprojection on the concave surface of the first component and a centralopening in the convex surface of the intermediate component, the centralprojection positionable within the central opening to prevent lateralseparation of the intermediate component and the first component. 25.The arthroplasty implant according to claim 24 wherein the concavesurface of the first component is bounded by a first peripheral edge andthe convex surface of the intermediate component is bounded by a secondperipheral edge, the first peripheral edge contacting the secondperipheral edge when relative movement between the first component andthe intermediate component reaches a maximum limit.
 26. The arthroplastyimplant according to claim 15 wherein one of the first component and theintermediate component includes a laterally outwardly facing projectionand the other of the first component and the intermediate componentincludes a laterally inwardly facing recess, the projection interactingwith the recess to prevent lateral separation of the intermediatecomponent and the first component.
 27. The arthroplasty implantaccording to claim 15 wherein the first component includes an annularwall bounding the concave surface of the first component, the annularwall being formed with an annular undercut defining a laterally inwardlyfacing recess, and the intermediate component includes an annular ribdefining a laterally outwardly facing projection, interaction betweenthe annular rib and the annular undercut preventing lateral separationof the intermediate component and the first component.
 28. Thearthroplasty implant according to claim 15 wherein the first componentis a phalangeal component of a metatarsophalangeal joint implant and isconnectable to a phalanx, and the second component is a tarsal componentof the metatarsophalangeal joint implant and is connectable to a tarsus.29. The arthroplasty implant according to claim 15 wherein the secondcomponent is movable with respect to the intermediate component inmutually orthogonal directions.
 30. An arthroplasty implant forproviding a joint between a first body member and a second body member,the arthroplasty implant comprising: a first component defining aconcave surface and having a first connector connecting the firstcomponent to the first body member; a second component defining a convexsurface and having a second connector connecting the second component tothe second body member; an intermediate component positioned between thefirst component and the second component and defining a convex surfaceslidable on the concave surface of the first component to allowarticulation between the first component and the intermediate componentand a concave surface slidable on the convex surface of the secondcomponent to allow articulation between the second component and theintermediate component; and a central projection formed on the concavesurface of the first component and a central opening formed in theconvex surface of the intermediate component, the central projectionpositionable within the central opening and preventing lateralseparation of the intermediate component and the first component. 31.The arthroplasty implant according to claim 30 wherein the concavesurface of the first component is bounded by a first peripheral edge andthe convex surface of the intermediate component is bounded by a secondperipheral edge, the first peripheral edge contacting the secondperipheral edge as relative movement between the first component and theintermediate component reaches a maximum limit.
 32. An arthroplastyimplant for providing a joint between a first body member and a secondbody member, the arthroplasty implant comprising: a first componentdefining a concave surface and having a first connector connecting thefirst component to the first body member; a second component defining aconvex surface and having a second connector connecting the secondcomponent to the second body member; an intermediate componentpositioned between the first component and the second component anddefining a convex surface slidable on the concave surface of the firstcomponent to allow articulation between the first component and theintermediate component and a concave surface slidable on the convexsurface of the second component to allow articulation between the secondcomponent and the intermediate component, one of the first component andthe intermediate component including a laterally outwardly facingprojection and the other of the first component and the intermediatecomponent including a laterally inwardly facing recess, the projectioninteracting with the recess and preventing lateral separation of theintermediate component and the first component.
 33. The arthroplastyimplant according to claim 32 wherein the first component includes anannular wall bounding the concave surface of the first component, theannular wall being formed with an annular undercut defining thelaterally inwardly facing recess, and the intermediate componentincludes an annular rib defining the laterally outwardly facingprojection, interaction between the annular rib and the annular undercutpreventing lateral separation of the intermediate component and thefirst component.
 34. The arthroplasty implant according to claim 32wherein the first connector and the second connector each includes acentral projecting post locatable in a hole formed in a respective bodymember.